The present invention relates to oral controlled release dosage formulations containing an analgesic. More specifically, the present invention relates to an oral dosage formulation in the form of a tablet comprising a nonsteroidal anti-inflammatory drug (NSAID), such as salicylic acid, indomethacin, ibuprofen, naproxen, naproxen sodium, flubiprofen, indoprofen, ketoprofen, piroxicam, diclofenac, etodolac, ketorolac or their pharmaceutically acceptable derivatives. Most preferably the NSAID is a pyranocarboxylic acid such as etodolac.
Numerous techniques are in the prior art for preparing sustained or controlled release pharmaceutical formulations. One common technique involves surrounding an osmotically active drug core with a semipermeable membrane. The drug is released from the core over time by allowing a fluid such as gastric or intestinal fluid to permeate the coating membrane and dissolve the drug so the dissolved drug can permeate the membrane. In some cases a hydrogel is employed to push the active ingredient through a passageway in the membrane. Some representative examples of these osmotic tablet systems can be found in U.S. Pat. Nos. 3,845,770, 3,916,899, 3,952,741, 4,034,758, 4,077,407 and 4,783,337.
Another common technique for preparing controlled release pharmaceutical formulations is to encapsulate a plurality of beads, pellets or tablets that are coated with varying levels of a diffusion barrier and/or different types of the diffusion barriers. Examples of these beaded formulations can be found in U.S. Pat. Nos. 5,376,384, 5,529,790, 5,470,584, 5,002,776, 5,445,829 and 5,578,321.
Still another common technique for preparing controlled release pharmaceutical formulations involve the use of a matrix or carrier base system wherein the active ingredient is mixed or dispersed throughout a controlled release substance. Examples of the carrier based system are described in U.S. Pat. Nos. 4,369,172, 4,389,393 and 4,966,768. U.S. Pat. No. 4,966,768 describes a carrier base controlled release pharmaceutical formulation containing etodolac and a release modifying agent. The carrier base described in U.S. Pat. No. 4,966,768 comprises a mixture of ethylcellulose and hydroxypropyl methylcellulose wherein the hydroxypropyl methylcellulose has an average molecular weight of less than 50,000 and a viscosity of 80 to 120 cps in a 2% aqueous solution.